The present invention relates to an apparatus and method for observing a radio hologram by a two-input interference observation method.
The inventor of this application has proposed an apparatus and method for observing a radio hologram in Japanese Patent Application Laid-Open Gazette No. 11-65405 entitled xe2x80x9cCircumference Scanning Type Hologram Observation Apparatus and Method Thereforxe2x80x9d (laid open Mar. 5, 1999, corresponding German Patent Application Laid-Open DE19838052A-1). As depicted in FIG. 1, a fixed antenna Ar and a rotary scanning antenna Am which is driven by a motor M are used, and the received signal from the antenna Am is received by a receiver Rm via a rotary joint JR, whereas the received signal from the fixed antenna Ar is received by a receiver Rr. The receivers Rm and Ar select and amplify signals of a preset frequency f, and output IF signals Sr(f) and Sm(xcfx86, f) (where xcfx86 is azimuth). These output signals Sr(f) and Sm(xcfx86, f) are applied to interference means 11, wherein they are caused to interfere with each other to obtain ∫Sr*(f). Sm(xcfx86, f) (where * indicates a complex conjugate), which is detected by a complex detector 12 to obtain measured data E(xcfx86). This data is stored in a buffer memory 21 for the rotational angle (horizontal azimuth) of the rotary scanning antenna Am. For the stored result a calculation/display part 22 performs a computation to reconstruct a hologram and displays the result of computation.
By carrying out the hologram measurement as described above, it is possible to obtain a viewing angle over the entire range of 360 degrees with no blind spots.
Because of mechanical driving of the antenna Am for rotary scanning, the above apparatus is incapable of making fast hologram observations. Another disadvantage is susceptibility to unstable reflected and/or diffracted waves.
It is therefore an object of the present invention to provide a radio hologram observation apparatus and method that permit fast hologram observation.
Another object of the present invention is to provide a radio hologram observation apparatus and method that permit stable measurements unaffected by fading.
Still another object of the present invention is to provide a dipole antenna which is simple-structured and suitable for mass production and a manufacturing method which permits easy fabrication of dipole antennas of uniform characteristics..
According to an aspect of the present invention, there is provided a hologram observation apparatus which includes a cascade connection of a plurality of antenna select means for selecting at least one of received signals of antenna elements of a ring-shaped array antenna and a plurality of receiver select means for supplying the selected received signal to any one of a plurality of receivers and in which: the received signal from the selected antenna element is provided to a selected one of the receivers; received signals from other selected antenna elements are provided to another one of the receivers; and the outputs from the two receivers are combined as a reference signal for interference with the output from another receiver to conduct hologram observations.
The receiver for providing the reference signal output receives, as a synthetic directional pattern, a combined version of received signals from a plurality of antenna elements. The antenna elements are selected so that the main lobe of the synthetic directional pattern is set in the direction of arrival of a radio wave and the null in the direction of arrival of a reflected and/or diffracted wave.
The selective supply of the antenna element received signal to the receiver which provides the reference signal output is fixed, and the observation is made of the interference between received signals while sequentially switching the selective application of antenna element received signal to the other receiver.
According to another aspect of the present invention, there is provided a dipole antenna which comprises: a tubular feeding part and first and second antenna parts formed in one piece of an insulating material, the first and second antenna parts being extended from one end of the feeding part in opposite directions and having a length nearly equal to xc2xc of the effective wavelength xcex; a first antenna element formed by a metal-plated layer all over the first antenna part and extending to the edge of a through hole of the feeding part; a second antenna element formed by a metal-plated layer all over the second antenna part; a through hole formed by a metal-plated layer deposited all over the interior surface of the through hole and connected to the first antenna element; an outer conductor formed by a metal-plated layer deposited all over the outer peripheral surface of the feeding part and connected to the first and second antenna elements; a pair of slits cut in the outer conductor lengthwise thereof between the first and second antenna elements, the pair of slits extending a length about xcex/4 from one end of the feeding part; and a connector part formed at the other end portion of the feeding part.
According to another aspect of the present invention, a reflector part is formed integrally with the feeding part and the first and second antenna parts such that it is spaced about xcex/4 apart from said first and second antenna parts of the feeding part, contiguous to or away from said pair of slits and substantially vertical to the feeding part and that the feeding part lies at the center of the reflector part, and a reflector layer is formed by a metal-plated layer over the entire surface area of either side of the reflector part and connected to the outer conductor.
According to the antenna manufacturing method of the present invention, the above-mentioned antenna portion made of an insulating material is molded in one piece, then the entire area of the mold surface is given metal plating, and the plating is partly removed to form a balun of the external conductor with first and second antenna elements and a xcex/4 long slit.